问在1883端口上订阅MQTT是否安全？

EN

#include <ESP8266WiFi.h>
#include "Adafruit_MQTT.h"
#include "Adafruit_MQTT_Client.h"

/************************* WiFi Access Point *********************************/

const char* WLAN_SSID = "SSID";
const char* WLAN_PASS = "password";

/************************* Adafruit.io Setup *********************************/

#define AIO_SERVER      "mqtt.gbridge.io"
#define AIO_SERVERPORT  1883                   // use 8883 for SSL
#define AIO_USERNAME    "gbridge-username"
#define AIO_KEY         "mqqt password"

/************ Global State (you don't need to change this!) ******************/

// Create an ESP8266 WiFiClient class to connect to the MQTT server.
WiFiClient client;
// or... use WiFiFlientSecure for SSL
//WiFiClientSecure client;

// Setup the MQTT client class by passing in the WiFi client and MQTT server and login details.
Adafruit_MQTT_Client mqtt(&client, AIO_SERVER, AIO_SERVERPORT, AIO_USERNAME, AIO_KEY);

/****************************** Feeds ***************************************/

// Setup a feed called 'photocell' for publishing.
// Notice MQTT paths for AIO follow the form: <username>/feeds/<feedname>
Adafruit_MQTT_Publish onoffset = Adafruit_MQTT_Publish(&mqtt,"on off set link");

// Setup a feed called 'onoff' for subscribing to changes.
Adafruit_MQTT_Subscribe onoffbutton = Adafruit_MQTT_Subscribe(&mqtt,"on off link");